When I tried to connect DBSRX2
to RXB or RXA the it wasn't detected. I mean when I ran usrp_probe the
model shown was 'unkown' and frequency range was from -9000000.0 to
9.000000. Any help what I need to do in order to check the DBSRX2
?

DBSRX2 is only supported under UHD, not under the "classic" drivers.
If you run:

uhd_usrp_probe --args "type=usrp1"

You'll find that it can cope with the DBSRX2 just fine. Since you're a
new user of this gear, without any
necessity of backwards compatibility with older software, you should
be using UHD exclusively.

I downloaded UHD from link above, then I did
following.

cd UHD.

cd host

mkdir build

cd build

cmake ../

make

make install

ldconfig

But then when I
ran uhd_find_devices I got following output:

"Ignoring discovered device RuntimeError: Expected protocol
compatibility number 9, but got 7: The firware build is not compatible
with the host code build.

No UHD Devices Found"

Lights D and F are on the N210. No other lights.

Another question what is minimum speed required for
LAN(Etherenet) interface on PC ? 100Mbps or 1000Mbps ?

The ethernet-connected devices (USRP2, N2XX) require 1 GiGe--they won't
work at any other rate.